Light Emmitting Diode (LED)
A semiconductor device which emits light. Under an applied current, electrons move between energy states in dissimilar semiconductor materials fabricated in adjacent layers within the device, releasing some of this energy as light by spontaneous emission. Emission is typically of one color but the device has a fairly broad output across a spectrum of ~50nm. The output is not coherent (i.e. non-laser light).
Devices based on GaAs or AlGaAs typically emit around 830nm, while InGaAsP and InP devices are often more suitable for telecoms wavelengths, e.g. 1310nm or 1550nm. Typical LED outputs are typically a few mW of power, while a superluminescent LED is a more high power device and output may be a few 100mW.